Classes and interfaces without a backslash \ inside their fully-qualified name must be fully qualified

Problem/Motivation

This has been a discussion point in the MR's of our team for our projects. Mainly about functions calls like \Drupal:: in none name-spaced files (e.g. .module, .install, .api,...).

I would usually write my code with the leading backslash.

$facet_manager = \Drupal::service('facets.manager');

But then a team member would come in saying the leading backslash is not required as we're not in a namespace. Looking at Drupal core, I can see a mix of both being used, so I think it's good if we could standardise this as a standard.

Core example where it is done with a \ : https://git.drupalcode.org/project/drupal/-/blob/11.x/core/modules/autom...

Core example where it is done withouth a \ : https://git.drupalcode.org/project/drupal/-/blob/11.x/core/modules/toolb...

Happy to say thought that there are not that many cases without the \ in Drupal Core. I did a code search today on the 11.x branch in PHPStorm (since it's not possible to search on Drupal:: with GitLab code search) and only found 2 code occurrences. Screenshot attached.

Benefits

By enforcing this change, function calls like \Drupal:: are written the same everywhere when not in a namespace.

Three supporters required

1. https://www.drupal.org/u/borisson_ (2025-01-23)
2. https://www.drupal.org/u/drunken-monkey (2025-01-23)
3. https://www.drupal.org/u/sophie.sk (2025-02-21)
4. https://www.drupal.org/u/Kingdutch (2026-04-28)

Proposed changes

Provide all proposed changes to the Drupal Coding standards. Give a link to each section that will be changed, and show the current text and proposed text as in the following layout:

1. Namespaces » Using classes

Current text

Classes and interfaces without a backslash \ inside their fully-qualified name (for example, the built-in PHP Exception class) must be fully qualified when used in a namespaced file. For example: new \Exception();. Do not use global classes.

Proposed text

Classes and interfaces without a backslash \ inside their fully-qualified name (for example, the built-in PHP Exception class) must be fully qualified. For example: new \Exception();. Do not use global classes.

2. Repeat the above for each page or sub-page that needs to be changed.

Remaining tasks

1. Create this issue in the Coding Standards queue, using the defined template
2. Add supporters
3. Create a Change Record
4. Review by the Coding Standards Committee
5. Coding Standards Committee takes action as required
6. Discussed by the Core Committer Committee, if it impacts Drupal Core
7. Final review by Coding Standards Committee
8. Documentation updates
   1. Edit all pages
   2. Publish change record
   3. Remove 'Needs documentation edits' tag
9. If applicable, create follow-up issues for PHPCS rules/sniffs changes

For a full explanation of these steps see the Coding Standards project page